Hello BubbaMD
Interlaken is a convenient travel hub, but it’s not a great place to stay; it is neither a mountain resort nor at the lake. The tired tourist town is popular with tourists from India and the Middle East because there are many restaurants that cater to their needs. Personally, I won’t be staying in Interlaken; it is not Swiss.
Given your itinerary, I would still opt for the Swiss Travel Pass or the Swiss Half Fare Card plus individual tickets or local passes.
I suggest that you should finish your trip planning before you even lose a thought on the ticket options. The ticket decision should be the very last step of your trip planning.
Also, on 17 April, it is impossible to do Harder Kulm and Jungfraujoch on the same day. Same for 18 April, Gornergrat and Matterhorn Glacier Paradise. Each excursion needs at least half a day.
From my point of view, your trip planning looks rather like a wish list yet a reasonable trip planning. Use www.sbb.ch/en to verify your plans, and to get an idea of the travel time needed. Our country is small, but high mountains make travel often cumbersome. Furthermore, daylight in April is not lasting for that long at night, mountain railways and cable cars stop their services early.
Easter does not have a great impact on your travel; Good Friday, Easter Sunday, as well as Easter Monday are holidays, public transport runs according to Sunday schedule and most grocery stores and other shops remain closed. In the mountains, Easter is still considered winter, locals use the days to go skiing.
I suggest posting your post in the TripAdvisor Switzerland forum for more insights on the trip planning. It is run by local destination experts. Here in the SBB Community, we limit our advice to travel and ticket questions, as we are public transit travel experts.
https://www.tripadvisor.com/ShowForum-g188045-i336-Switzerland.html
Kind regards,
Roland